Workers in the herein related prior art understand the term "metallic `tubing` type heat exchanger" to mean:
(a) the heat exchanger includes elongate heat-conductive metallic "tubing" having two open-end terminii. Extending between the open-end terminii, a visually-hidden inner-surface surrounded by an outer-surface. Such "tubing" can take numerous forms (e.g. regular-size tubes, confronting contoured plates, etc.); and wherein PA0 (b) it is intended (and inherently possible) that an inner-fluid and an outer-fluid, simultaneously flowing along the heat-conductive metallic "tubing" inner-surface and outer-surface, respectively, will have their temperatures conductively modified by each other.
Normal metallic fatigue eventually results in pinholes, cracks, or other breach of the heat exchanger's elongate heat-conductive metallic "tubing", whereby inter-fluids seepage results between the inner-fluid and outer-fluid. If it is essential that one (or both) of the two flowable fluids be strictly maintained free of inter-fluids contamination (e.g. milk or other foodstuff inner-fluid, and steam or coolant outer-fluid), such inter-fluids seepage is intolerable. Thus, the heat exchanger's elongate metallic heat-conductive "tubing" must be regularly periodically inspected to detect the possible emergence of structural breach between the "tubing" inner-surface and outer-surface.